What is a LOPA?
LOPA stands for Layer
of Protection Analysis
LOPA is a process to
evaluate risk with explicit
risk tolerance for a
specific consequence
It’s about creating value
without taking
unnecessary risk
The level of risk
acceptance is expressed
in terms of tolerable
frequency
Tolerable frequency is a
decision criteria
The higher the
consequence…
the lower the
tolerable
frequency
Single fatality risk tolerance*
0.01% per year
Compared to…
Multiple fatality risk tolerance*
0.001% per year
*Generalized risk tolerance in an industrial environment
Let’s try to make these
numbers resonate with
some relativity
Driving fatality
0.01% per year
(i.e. same as the
acceptable risk
for industrial
work
environment)
[NIOSH 1997]
Alaska crab fishing
fatality
0.356% per year
(i.e. 35x the
acceptable risk for
industrial work
environment)
[NIOSH 1997]
Do you know the
tolerable frequency of
for your company?
If so, who decide how
much risk your company
can take on? Are the
decisions consistent across
the company?
Lets break down the
LOPA into seven steps:
Step 1: Identify a single
consequence to analyze
In our example, the reboiler condensate pot
can overpressure
leading to vessel rupture
and resulting in a single
fatality
D-101 Re-boiler Condensate Pot
PSV
111
Size ½
SET @ 700kPag
To atmosphere at safe
location
Steam
D-101
Drawing Ref.
3/4”
LT
253
2”
3”
HLL=2550 mm
NLL=1650 mm
PG
253
LLL=250 mm
LC
2”
3”
253
3/4”
LY
253
6”
LV
253
6”
Condensate
6”
6”
Drawing Ref.
6”
Step 2: Define the
tolerable frequency for
the consequence
Multiple
• 0.001%/year
Fatality
Single
Fatality
Hospitalized
Injury
•0.01%/year
• 0.1%/ year
Step 3: Assess the
probability of the
initiating events
The level control valve
can fail in the closed
position leading to
overpressure
D-101 Re-boiler Condensate Pot
PSV
111
Size ½
SET @ 700kPag
To atmosphere at safe
location
Steam
D-101
Drawing Ref.
3/4”
LT
253
2”
3”
HLL=2550 mm
NLL=1650 mm
PG
253
LLL=250 mm
LC
2”
3”
253
3/4”
LY
253
6”
LV
253
6”
Condensate
6”
6”
Drawing Ref.
6”
Let’s say this control loop has a
0.1 probability (10% chance) of
failure per year
Step 4: Identify
independent protection
layers and assign a risk
reduction factor
Important!
Each protection layer must
be independent from the
initiating event and
independent from other
safeguards
D-101 Re-boiler Condensate Pot
PSV
111
Size ½
SET @ 700kPag
To atmosphere at safe
location
Steam
D-101
Drawing Ref.
3/4”
LT
253
2”
3”
HLL=2550 mm
NLL=1650 mm
PG
253
LLL=250 mm
LC
2”
3”
253
3/4”
LY
253
6”
LV
253
6”
Condensate
6”
6”
Drawing Ref.
6”
Let’s say the pressure safety
valve will reduce the
likelihood of rupture by 100
or you can say…
Risk Reduction of 100
you can also say…
the Probability of Failure on
Demand of 0.01
Step 5: Calculate the new
expected frequency of the
consequence
Expected frequency = initiating
events frequency x probability
of failure of the safeguard
New expected frequency = 0.001
(0.1 valve failure per year x 0.01
probability of safety valve
failure)
D-101 Re-boiler Condensate Pot
PSV
111
Size ½
SET @ 700kPag
To atmosphere at safe
location
Steam
D-101
Drawing Ref.
3/4”
LT
253
2”
3”
HLL=2550 mm
NLL=1650 mm
PG
253
LLL=250 mm
LC
2”
3”
253
3/4”
LY
253
6”
LV
253
6”
Condensate
6”
6”
Drawing Ref.
6”
Given a person will be around the
vessel when ruptured…
Our expected frequency of a
fatality in this scenario is 0.001 per
year
Or
0.1% chance of a fatality per year
D-101 Re-boiler Condensate Pot
PSV
111
Size ½
SET @ 700kPag
To atmosphere at safe
location
Steam
D-101
Drawing Ref.
3/4”
LT
253
2”
3”
HLL=2550 mm
NLL=1650 mm
PG
253
LLL=250 mm
LC
2”
3”
253
3/4”
LY
253
1/1000 chance
a fatality per
year
6”
LV
253
6”
Condensate
6”
6”
Drawing Ref.
6”
Step 6: Decide if risk is
acceptable based on the
tolerable frequency
Expected
frequency
of a single
fatality =
0.001/year
Tolerable
frequency
of a single
fatality =
0.0001/year
That’s 10 times
more
likely than the maximum
frequency your company can
accept for a single fatality
Step 7: Determine
additional safeguards to
reduce the risk
Let’s add a high pressure
shutdown to the inlet as
a safeguard
D-101 Re-boiler Condensate Pot
PSV
111
XV
253
Size ½
SET @ 700kPag
To atmosphere at safe
location
Steam
D-101
Drawing Ref.
LT
253
2”
3”
HLL=2550 mm
HH
NLL=1650 mm
PT
253
LLL=250 mm
LC
2”
3”
253
LY
253
6”
LV
253
6”
Condensate
6”
6”
Drawing Ref.
6”
This safeguard consist of a
pressure sensor, logic
solver (independent from
the level control) and a
valve as a final element
This safeguard is a safety
instrumented function
(SIF)
XV
253
PT
253
Since we need to reduce the
risk by a factor of 10…
The probability of failure on
demand of the safety
instrumented function must
be less than 0.1
Or you can say the
safety instrumented
function must meet the
requirements of safety
integrity level 1
This safety instrumented
function is at SIL 1
XV
253
PT
253
Expected frequency with the new
safeguard
= 0.1 probability of valve failure
per year
x 0.01 probability of safety valve
failure
x 0.1 probability of the safety
instrumented function failure
=0.0001/year
New
expected
frequency
of a single
fatality =
0.0001/year
Tolerable
frequency
of a
single
fatality =
0.0001/year
Now the risk is
acceptable
Adding a safety
instrumented function is
one option to meet the
tolerable frequency.
Is it a good decision? Is
there a better option?
Any Questions?
Risk. Inspired.
For more lessons go to
www.icarus-orm.com